﻿//岛屿的最大面积(medium): https://leetcode.cn/problems/max-area-of-island/description/
class Solution {
public:
    int ret,sum;
    int m,n;
    bool vis[50][50];
    int dx[4] = {0, 0, 1, -1};
    int dy[4] = {1, -1, 0, 0};
    queue<pair<int,int>> q;
    int maxAreaOfIsland(vector<vector<int>>& grid) {
        m=grid.size(),n=grid[0].size();
        for(int i=0;i<m;i++)
        {
            for(int j=0;j<n;j++)
            {
                if(!vis[i][j]&&grid[i][j]==1)
                {
                    sum=0;
                    bfs(grid,i,j);
                    ret=ret>sum?ret:sum;
                }
            }
        }
        return ret;
    }
    void bfs(vector<vector<int>>& grid,int i,int j)
    {
        sum++;
        vis[i][j]=true;
        q.push({i,j});
        while(q.size())
        {
            auto [a,b]=q.front();
            q.pop();
            for(int k=0;k<4;k++)
            {
                int x=a+dx[k];   int y=b+dy[k];
                if(x>=0&&x<m&&y>=0&&y<n&& !vis[x][y]&&grid[x][y]==1)
                {
                    bfs(grid,x,y);
                }
            }
        }
    }
};

//被围绕的区域(medium): https://leetcode.cn/problems/surrounded-regions/description/
class Solution {
public:
    int m,n;
    int dx[4] = {0, 0, 1, -1};
    int dy[4] = {1, -1, 0, 0};
    queue<pair<int,int>> q;
    void solve(vector<vector<char>>& board) {
        m=board.size(),n=board[0].size();
        for(int i=0;i<m;i++)   
        {
            if(board[i][0]=='O') bfs(board,i,0);
            if(board[i][n-1]=='O') bfs(board,i,n-1);
        }
        for(int j=0;j<n;j++)
        {
            if(board[0][j]=='O') bfs(board,0,j);
            if(board[m-1][j]=='O') bfs(board,m-1,j);
        }
        for(int i=0;i<m;i++)
        {
            for(int j=0;j<n;j++)
            {
                if(board[i][j]=='.')    board[i][j]='O';
                else if(board[i][j]=='O')  board[i][j]='X';
            }
        }
    }
     void bfs(vector<vector<char>>& board,int i,int j)
    {
        board[i][j]='.';
        q.push({i,j});
        while(q.size())
        {
            auto [a,b]=q.front();
            q.pop();
            for(int k=0;k<4;k++)
            {
                int x=a+dx[k];   int y=b+dy[k];
                if(x>=0&&x<m&&y>=0&&y<n &&board[x][y]=='O')
                {
                    bfs(board,x,y);
                }
            }
        }
    }
};